Optimizing Thermal Efficiency of a Multi-Cylinder Heavy Duty Engine with E85 Gasoline Compression Ignition 2019-01-0557

Gasoline compression ignition (GCI) using a single gasoline-type fuel for direct/port injection has been shown as a method to achieve low-temperature combustion with low engine-out NOx and soot emissions and high indicated thermal efficiency. However, key technical barriers to achieving low temperature combustion on multi-cylinder engines include the air handling system (limited amount of exhaust gas recirculation (EGR)) as well as mechanical engine limitations (e.g. peak pressure rise rate). In light of these limitations, high temperature combustion with reduced amounts of EGR appears more practical. Previous studies demonstrated that the port and direct injection strategy exhibited the best performance, but the early heat release prevented the further increase in premixed fuel fraction and efficiency. In this work, experimental testing was conducted on a 12.4 L multi-cylinder heavy-duty diesel engine operating with high temperature GCI combustion using E85 gasoline. The impact on engine performance and emissions was evaluated at an engine speed of 1038 rpm and brake mean effective pressure (BMEP) of 1.4 MPa with port and direct injection strategy. Compared to previous gasoline results, the start of combustion was obviously retarded and premixed combustion was increased by E85. The combustion phasing, premixed fuel amount, and pumping loss were optimized to improve efficiency by adjusting main/pilot injection timing, port/pilot injection mass fraction, and turbo-charger setting. Overall, the brake thermal efficiency (BTE) of E85 was 1.2% and 0.5% higher than that of diesel baseline and E85/diesel dual fuel combustion. E85 showed nearly zero soot emissions and more than 70% less NOx emissions compared to diesel.